1. Field of the Invention
This invention relates to a pipe for use in systems which work with hot gases, i.e., for example, as the centre-pipe in a cyclone for the cleaning of hot gases or the reaction chamber in a fluid-bed installation.
2. Description of the Related Art
For the separation of particles from currents of air, the use is known, for example, of one or more cyclones. A cyclone consists of an upper, cylindrical part and a lower conical part. The air flow is introduced tangentially at the head of the cylindrical part, and continues in a downwardly-directed spiral movement. This is the so-called primary vortex, which continues down towards the nose of the conical part. From here, an upwardly-directed spiral movement emanates, namely the so-called secondary vortex. This leaves the cyclone through an axial outlet, the so-called centre-pipe, at the head of the cyclone.
For reasons of the vortical motion, the particles in the air current are influenced by strong centrifugal forces, whereby they are forced outwards towards the wall of the cyclone. From here they fall downwards towards the nose and are collected in a large container, said container either being changed at suitable intervals or continuously emptied through a sluice.
During the process of lime burning or in the manufacture of cement, it is desirable to clean the discharge air from the rotary kiln. A cyclone would be suitable for such cleaning, but commonly-known cyclones of metal have the disadvantage that the hot discharge gases will ruin the centre-pipe, in that said centre-pipe lies precisely in the path of the flow of hot gases and can be cooled only with great difficulty. The weldings in the centre-pipe will rupture, and the output from the cyclone gets blocked by falling material. Furthermore, the cyclone will, of course, be ruined. It has been shown that even metal alloys with high melting points have difficulty in withstanding the hot gases.
Moreover, to produce a centre-pipe of such alloy is very costly, in that a centre-pipe for a cyclone for the cleaning of discharge gases from a rotary kiln can, for example, have a diameter of 2-3 meters and a length of 1-2 meters.
Fluid-bed systems are installations in which the particle-formed material is held floating in an upwardly-directed flow of air. Such installations are used, for example, in the burning of lime and for other applications where it is desired to expose such materials to high temperatures, the reason being that when the material is held in a floating state, it has a very great effective surface.
With such systems, one meets the same problems as those encountered with centre-pipes for cyclones. The material must be held floating in a reaction chamber, and this must be capable of withstanding very high temperatures.